The present invention is directed to an imaging apparatus and process. More specifically, the present invention is directed to an imaging apparatus and process wherein an electrostatic latent image is formed on an imaging member and developed with a toner, followed by transfer of the developed image to an intermediate transfer element and subsequent transfer with very high transfer efficiency of the developed image from the intermediate transfer element to a permanent substrate, wherein the intermediate transfer element has a charge relaxation time of no more than about 2.times.10.sup.2 seconds.
The formation and development of images on the surface of photoconductive materials by electrostatic means is well known. The basic electrophotographic imaging process, as taught by C. F. Carlson in U.S. Pat. No. 2,297,691, entails placing a uniform electrostatic charge on a photoconductive insulating layer known as a photoconductor or photoreceptor, exposing the photoreceptor to a light and shadow image to dissipate the charge on the areas of the photoreceptor exposed to the light, and developing the resulting electrostatic latent image by depositing on the image a finely divided electroscopic material known as toner. The toner will normally be attracted to those areas of the photoreceptor which retain a charge, thereby forming a toner image corresponding to the electrostatic latent image. This developed image may then be transferred to a substrate such as paper. The transferred image may subsequently be permanently affixed to the substrate by heat, pressure, a combination of heat and pressure, or other suitable fixing means such as solvent or overcoating treatment.
Other methods for forming latent images are also known, such as ionographic methods. In ionographic imaging processes, a latent image is formed on a dielectric image receptor or electroreceptor by ion deposition, as described, for example, in U.S. Pat. Nos. 3,564,556, 3,611,419, 4,240,084, 4,569,584, 2,919,171, 4,524,371, 4,619,515, 4,463,363, 4,254,424, 4,538,163, 4,409,604, 4,408,214, 4,365,549, 4,267,556, 4,160,257, and 4,155,093, the disclosures of each of which are totally incorporated herein by reference. Generally, the process entails application of charge in an image pattern with an ionographic writing head to a dielectric receiver that retains the charged image. The image is subsequently developed with a developer capable of developing charge images.
Many methods are known for applying the electroscopic particles to the electrostatic latent image to be developed. One development method, disclosed in U.S. Pat. No. 2,618,552, is known as cascade development. Another technique for developing electrostatic images is the magnetic brush process, disclosed in U.S. Pat. No. 2,874,063. This method entails the carrying of a developer material containing toner and magnetic carrier particles by a magnet. The magnetic field of the magnet causes alignment of the magnetic carriers in a brushlike configuration, and this "magnetic brush" is brought into contact with the electrostatic image bearing surface of the photoreceptor. The toner particles are drawn from the brush to the electrostatic image by electrostatic attraction to the undischarged areas of the photoreceptor, and development of the image results. Other techniques, such as touchdown development, powder cloud development, and jumping development are known to be suitable for developing electrostatic latent images.
Imaging processes wherein a developed image is first transferred to an intermediate transfer means and subsequently transferred from the intermediate transfer means to a substrate are known. For example, U.S. Pat. No. 3,862,848 (Marley), the disclosure of which is totally incorporated herein by reference, discloses an electrostatic method for the reproduction of printed matter in which an electrostatic latent image is developed by the attraction of electroscopic marking particles thereto and is then transferred to a first receptor surface by the simultaneous application of contact and a directional electrostatic field of a polarity to urge the marking particles to the receptor surface, with the image then being transferred from the first receptor surface to a second receptor surface by the simultaneous application of contact and a directional electrostatic field of opposite polarity to urge the marking particles to the second receptor surface.
In addition, U.S. Pat. No. 3,957,367 (Goel), the disclosure of which is totally incorporated herein by reference, discloses a color electrostatographic printing machine in which successive single color powder images are transferred, in superimposed registration with one another, to an intermediary. The multi-layered powder image is fused on the intermediary and transferred therefrom to a sheet of support material, forming a copy of the original document.
Further, U.S. Pat. No. 4,341,455 (Fedder), the disclosure of which is totally incorporated herein by reference, discloses an apparatus for transferring magnetic and conducting toner from a dielectric surface to plain paper by interposing a dielectric belt mechanism between the dielectric surface of an imaging drum and a plain paper substrate such that the toner is first transferred to the dielectric belt and subsequently transferred to a plain paper in a fusing station. The dielectric belt is preferably a material such as Teflon or polyethylene to which toner particles will not stick as they are fused in the heat-fuser station.
Additionally, U.S. Pat. No. 3,537,786 (Schlein et al.), the disclosure of which is totally incorporated herein by reference, discloses a copying machine using a material capable of being persistently internally polarized as the latent image storage means. A removable insulative carrier is applied to the storage means and receives a toner which clings to the carrier in correspondence with a previously applied image pattern. The carrier is then removed from contact with the storage means and forms a record of the recorded image. In one embodiment, the insulative carrier is then passed over a heater to fix the toner so that the insulative carrier forms the final image bearing means. In an alternative embodiment, the insulative carrier bearing the toner is brought into contact with a separate image bearing medium so as to transfer the toner to this image bearing medium which then acts as the final image bearing means. The insulative carrier can be of a material such as polyethylene, polypropylene, polyethylene glycol terephthalate (Mylar.RTM.), polyeterafluoroethylene (Teflon.RTM.), polyvinylidene-acrylonitrile copolymers (Saran.RTM.), cellulose nitrate, cellulose acetate, acrylonitrile-butadiene-styrene terpolymers, cyclicized rubbers, and similar irradiation transparent, essentially non-photopolarizable organic or inorganic materials having a volume resistivity greater than 10.sup.9 ohm-cm.
U.S. Pat. No. 3,893,761 (Buchan et al.), the disclosure of which is totally incorporated herein by reference, discloses an apparatus for transferring non-fused xerographic toner images from a first support material, such as a photoconductive insulating surface, to a second support material, such as paper, and fusing the toner images to the second support material. Such apparatus includes an intermediate transfer member having a smooth surface of low surface free energy below 40 dynes per centimeter and a hardness of from 3 to 70 durometers. The intermediate transfer member can be, for example, a 0.1 to 10 mil layer of silicone rubber or a fluoroelastomer coated onto a polyimide support. The member can be formed into belt or drum configuration. Toner images are transferred from the first support material to the intermediate transfer member by any conventional method, preferably pressure transfer. The toner image is then heated on the intermediate transfer member to at least its melting point temperature, with heating preferably being selective. After the toner is heated, the second support material is brought into pressure contact with the hot toner whereby the toner is transferred and fused to the second support material.
In addition, U.S. Pat. No. 4,275,134 (Knechtel), the disclosure of which is totally incorporated herein by reference, discloses an electrophotographic process using a photosensitive medium having an insulating layer on a photoconductive layer, the surface of the photosensitive medium being uniformly charged with a primary charge. The primary-charged surface of the photosensitive medium is then charged with a charge of the opposite polarity or discharged and simultaneously therewith or therebefore or thereafter, exposed to image light from an original. A grid image is projected upon the surface of the suface of the photosensitive medium. For multi-color representation, the steps can be repeated in accordance with the number of colors desired. In this instance, the color images are transferred onto an intermediate drum which can be, for example, coated with a layer of Teflon.RTM..
Further, U.S. Pat. No. 4,682,880 (Fujii et al.), the disclosure of which is totally incorporated herein by reference, discloses a process wherein an electrostatic latent image is formed on a rotatable latent image bearing member and is developed with a developer into a visualized image. The visualized image is transferred by pressure to a rotatable visualized image bearing member. The steps are repeated with different color developers to form on the same visualized image bearing member a multi-color image which corresponds to one final image to be recorded. The latent image bearing member and the visualized image bearing member form a nip therebetween through whcih a recording material is passed so that the multi-color image is transferred all at once to a recording material.
U.S. Pat. No. 2,885,955 (Vyverberg) discloses an apparatus for printing on print-receiving material of a type liable to dimensional change or change in other physical characteristics when subjected to xerographic heat or vapor fixing techniques. The apparatus contains a rotatable xerographic cylinder having an image forming surface with a photoconductive layer and a means for rotating the cylinder through a predetermined path of movement relative to a plurality of xerographic processing stations, including a charging station for applying electric charge to the photoconductive layer, an exposure station with a projection means for projecting a light image onto the charge photoconductive layer to form an electrostatic latent image, and a developing station having a means for depositing powdered developing material on the photoconductive layer to develop the latent image. In addition, the apparatus contains a means for supporting a web of water receptive planographic printing material, a means for moving the web in surface contact with the photoconductive layer through a portion of its path of movement, a transfer means for transferring the developed image from the photoconductive layer to the web surface while the photoconductive layer and the web are in surface contact, a fixing means for fixing the developed image on the web surface, a means for applying an aqueous solution to the surface of the web, a means for applying lithographic ink to the fixed powder image on the web surface, a feeding means for feeding print receiving material into surface contact with the inked surface of the web, and a means for pressing the print-receiving material into intimate surface contact with the inked powder image on the web surface.
Further, U.S. Pat. No. 3,526,191 (Silverberg et al.) discloses a duplicating process wherein magnetic images of copy to be reproduced are created and used to attract magnetically attractable powder to form subsequent reproductions of the original copy. The magnetic images are deposited and fused to a sheet to form a master. The magnetic field extending from the master can be used to either attract magnetic toner directly to the fused image on the master with subsequent transfer to a copy sheet or the field can extend through a copy sheet placed over the master to attract magnetic toner to the copy sheet in the pattern of the master image. The toner images are then fused to the copy sheet. Mirror images can be avoided by transferring the toner images to intermediate surfaces or by producing the master in a reverse reading form.
Additionally, U.S. Pat. No. 3,804,511 (Rait et al.) and U.S. Pat. No. 3,993,484 (Rait et al.) disclose a process wherein an electrostatic image is formed on a surface and magnetic toner paticles are then applied to the surface and adhere thereto in correspondence with the electrostatic image. Portions of the same surface or another are surface are magnetized, as determined by the location of the toner particles, to form a magnetic image corresponding to the electrostatic image. The toner particles are then transferred by friction to a copy medium such as paper while the magnetic image is retained or stored on the surface. Toner particles can then again be applied to the magnetic image for production of additional copies.
"Color Xerography With Intermediate Transfer," J. R. Davidson, Xerox Disclosure Journal, volume 1, number 7, page 29 (July 1976), the disclosure of which is totally incorporated herein by reference, discloses a xerographic development apparatus for producing color images. Registration of the component colors is improved by the use of a dimensionally stable intermediate transfer member. Component colors such as cyan, yellow, magenta, and black are synchronously developed onto xerogaphic drums and transferred in registration onto the dimensionally stable intermediate transfer member. The composite color image is then transferred to a receiving surface such as paper. The intermediate transfer member is held in registration at the transfer station for transferring images from the xerographic drums to the member by a hole-and-sprocket arrangement, wherein sprockets on the edges of the drums engage holes in the edge of the intermediate transfer member.
Intermediate transfer elements employed in imaging apparatuses in which a developed image is first transferred from the imaging member to the intermediate and then transferred from the intermediate to a substrate should exhibit both good transfer of the developer material from the imaging member to the intermediate and good transfer of the developer material from the intermediate to the substrate. Good transfer occurs when most of all of the developer material comprising the image is transferred and little residual developer remains on the surface from which the image was transferred. Good transfer is particularly important when the imaging process entails generating full color images by sequentially generating and developing images in each primary color in succession and superimposing the primary color images onto each other on the substrate, since undesirable shifting and variation in the final colors obtained can occur when the primary color images are not efficiently transferred to the substrate.
Although known processes and materials are suitable for their intended purposes, a need remains for imaging apparatuses and processes employing intermediate transfer elements with high transfer efficiency. In addition, there is a need for imaging apparatuses and processes employing intermediate transfer elements that enable generation of full color images with high color fidelity. Further, a need exists for imaging apparatuses and processes employing intermediate transfer elements that enable a simplified paper path through the apparatus. Additionally, a need remains for imaging apparatuses and processes employing intermediate transfer elements that enable high speed printing processes for the generation of images of more than one color. There is also a need for imaging apparatuses and processes employing intermediate transfer elements that enable simplified and improved registration of superimposed images of different colors on a single substrate sheet to form multicolor or blended color images.